The object of this research proposal is to evaluate the function of sympathetic nervous system in young and adult SHR (Okamoto strain) by measuring the concentration of catecholamines, and their major metabolites and degradative enzymes in central and peripheral tissues. The recent development, in our laboratory, of sensitive radioenzymatic assays makes this new approach possible. With these assays we will determine in blood, mesenteric arteries, heart and specific brain nuclei the concentration of the following: epinephrine, norepinephrine and its major extraneuronal metabolite normetanephrine, and the major deaminated metabolites 3,4-dihydroxyphenylglycol and 3,4-dihydroxymandelic acid. In the same tissues the activity of the catecholamine degradative enzymes catechol-O-methyltransferase and monoamine oxidase, forms A and B, also will be determined. Our working hypothesis is that increased sympathetic function is responsible for hypertension in SHR and that the metabolic products will reflect this more accurately than the parent catecholamines.